Apparatus for use in evaluating gas reservoirs



J'. P. SLOAN July l0, 1945.

APPARATUS FOR USE IN EVALUATING GAS RESERVIRS 4 sheets-sheet 1 Filed Jan. 19, 1944 INVEN TOR. Paw 062 Zz,

gm q f a@ July 10, 1945- y J. P. sLoAN 2,380;082

APPARATUS FOR USE' IN EVALUATING GAS RESERVOIRS Filed Jan. 19, 1944 4 Sheets-Sheet 2 July 10, 1945 J. P. sLoAN 2,380,082

I APPARATUS FOR USE IN EVALUATING GAS RESERYOIRS Filed Jan. 19, 1944 4 Sheets-Sheet 3 672310 z a nuevas/Q0 z a 567aal0l20 2 a 4567 VOLUME /N CUB/c FEET INVENTOR. Jfau @loam July l0, 1945.- .1. P. sLoAN AIPARATUS FOR USE IN EVALUATING GAS RESERVOIR-S Filed Jan. 19, 1944 M m .f m w m m n n WAM m mmm m www m www wam .m NR www m 7m@ m Mmm .m i m @FE 60m w RNV www m MMH( m @ma ffm w w m w PRL-55ans /N Paz/Nas Pff? QI/AHEf/vcH 671055 I@ INVENTOR. J Pcz tloz,

mensuel, io, 1945 UNITED srs'rss PATENT. OFFICE assessemsas'rus Fon. Usa nv svsws'rmo ons assnnvoms Jam raul slm, nonnen, ',rex.,1 signor a Houston Laboratories; Houston, Tex., a corporation of Texas Application January 19,1944, anni No. nasse 9 Claims.

The invention relates to apparatus for use in evaluating the content of gas reservoirs, gas distillate reservoirs and the -sascap of oil reservoirs for planning the development of such reservoirs and determining the most eilicient operating conditions for the. production of these properties. MoreA speciiically the invention relates to improved apparatus for analyzing fluid from saidrecervoirs to? obtain information as to the complessibility f the gaseous phase and graphical data such as the behavior of the reservoir material under reservoirpressure and temperature and under reduced pressures and temperatures to make possible the most satisfactory and prontableproduction of the reservoir.

This application `is a continuation-impart of my copending application Serial No. 436,295. led March 26, 1942 and entitled Method of evaluating the content of gas reservoirs. In said application itfwas' explained that thgoevaluation ofthe hy- 'reservoir as a ve referred to residesA in d the volume of sas and vdistillate or other liquid hydrocarbons that can be ultimatelyy produced therefrom. It was further explained that the term "behavior as used herein refers to the -chanse in the composition oi the liquid and sas phases ot the reservoir material with any corresponding change in temperature and/or Natural-sas and petroleum are mixtures oi hyldrocarbons. the simplest or these being methane, composed oi one carbon atom surrounded by four 'hydrogen atoms. Theoretically, rthere is a denite compound identiiled as methane containing in'addition to hydrogen the one carbon atom, a second identined as ethane containing two caratome: Propane containing three carbon atomsand so on up to a deniteompound oi' forty carbon atoms.- As the chemical structure becomes more complex isomers are formed such as isobutane, lwhich is the isomer oi normal butane. All natural gases are composed of a mixl ture or the lighter hydrocarbons, and the crude oils, asphalte and tars are mixtures of the heavier ones. No two of these mixtures is identical in composition and from the enormous number oi possible compounds and the wide variation of their properties, it is easy to see the impossibility of analyzing each o`i these mixtures with ac curaey. `Both the time and the cost would be prohibitive. So,v forconveni ce theiight ends are analyzed by coolins and ractional distilla- Ition withscme decree of accuracy up throush .compounds containing six or seven carbon atoms. The boiling points oi' these compounds 'arejrela- -Hls-ss) s tively i'ar apart and they can be separated easily. The higher boiling compounds, whose boilins' points are successively closer together, are then lgrouped according to .boiling-range, and no ato tempt is made to separate the individual mem-l bers of these groups. Under atmospheric conditions oi temperature and pressure, the rst four hydrocarbons are in the gaseous state, the next three or tour are liq- A l0 uid hut highly volatile, the remainder are from relatively stable liquid vto solid. However, in the .natural reservoir,- quite a diierent set of conditions is present. fllhe temperatures are higher. ranging from 140" F. to approximatelyoo" l". theadvent of deeper drilling.` lhis increased temperature tends to vaporize the lighter portions o thenormally liquid hydrocarbon mixture described' above and to convert the normallyy solid Daraillnes and tarry portions to the liquid state. The pressures in these reservoirs range from a. few pounds per squareinch above atmospheric pressure to "approximately six thousand pounds per square inch. These pressures tend to reverse the vaporization eiect of the elevated temperatures and to reliquify the ethane to' octane group and to force the methane into solution in the 'liquida This stripping ofthe ethane-plus portions of the gas by increasing,

pressure continues until the pressures reach approximately nine hundred to one thousand pounds per square inch. In this region the process of squeezing the ethane-plus materials out oi.' the methane-comes to a halt, and as the pressure i further increases a reversal sets in. .From here on, the ethane plus material begins to reenter the vapor phase, the lighter materials in larger quanf titles than theA heavier. This process continues,

with successively heavier materials going into'the tered. nMany ot these gases contain signincant quantities of the heavier hydrocarbons held in `is the vapor phase by virtue of thepeurc nd with even higher temperatures in prospect with vapor phase as the pressure-continues to rise. This phenomenon is known as retrograde -vatemperature of the reservoir. In the normal production of these reservoirs, as part of the gas content is withdrawn the pressure upon the remainder is lowered. 'IAhis lowering of pressure on the remaining reservoir fluid causes a condensation of some of the heavier hydrocarbons. Continued `withdrawals of material causes a continuing condensation until the pressure in the.

reservoir drops to approximately one thousand pounds :per square inch. The liquid condensate thusprecipitated serves 'to wet the surrounding sand body and is thereby forever lost.

There has been developed in recent years a system of operation known as cycling or recycling, which is designed to prevent this irretriev- L able loss of material in these -condensate or distillate reservoirs. In this process. gas is withdrawn from a well in one part of the field, transmitted by pipe lines to a plant, and there processed by means of pressure'reduction and absorption for the removal of the conden'sable portions of material, the residual gas being then recompressed to above formation pressure, and reinjected into another part of the reservoir. This procedure tends to maintain approximately the original reservoir pressure and thereby prevents the liquid material composed of gasoline and kerosene fractions is recovered for immediate sale and the excess gas is conserved for future use.

The volume of the recoverable liquid'varies lwidely with diierent reservoirs. The 'rates at which it is condensed by pressure reduction is a function of the particular composition of the material in the reservoir. Therefore, i'n order for the owners to know whether or not the loss of this liquid by normal withdrawal ofthe reservoir contents justifies recycling, it is necessary that they know the behavior of the material in the reservoir under reservoir temperature and diminishing pressure. Such information would enable the owners to make a decision as to recycling, absorption, or a. simple separation operation as the most profitable method of producing the reservoir. A knowledge of the behavior' of the reservoir material at both a reduced pressure and a reduced .temperature would enable the owners to independently plan a programl for handling the material after it is brought to the surface, such as separator pressuresI absorption pressures, etc. Compressibility data would enable him to select the proper pipe line size, compressor volumes, or

l any place in the operation where he might lbe dealing with pressure-volume-temperature relationships and to more closely estimate his reserve l y i of liquid and gas and the reservoir energy available for the production of the reservoir.

An object of the invention is to provide apparatus wherein samples of the liquid and gas comprising the reservoir fluid of a stabilized well can be analyzed and. recombined in certain desired ratios of volume of liquid to volume of gas whereby to secure desirable information pertaining to said reservoir fluid.

Another object resides in provision of ap-V paratus including a variable volume cell within which the liquid and gas samples are recombined. The combination of liquid and gas thus produced represents the reservoir fluid entering 'the well' tubing. The apparatus of the invention is capable of operation at a constant temperature and the precipitation of the heavier hydrocarbons; also for bringing the gas-liquid mixture to equilib-A mostatic control for the apparatus so A'that any number of isothermal pressure-liquid volume l curvesmay be obtained without disturbing the the field separator. I'his compressibility data isof value 'in calculating the equivalent amountof the liquid to be added to a definite volume 0f the gas to obtain an equivalent mixture to that which entered the well bore from the formation during sampling. The advantage of this step in the present method resides in the fact that the calculations are made on the basis of the actual determined compressibility of the gas. With these and various other objects in view,

the invention may consist of certain novel features of construction and operation, as will be more fully described and particularly pointed out in the specification, drawings and claims appended hereto.

In the drawings which illustrate an embodiment of the device, and wherein like referencel characters are used to designate like parts- .Figure 1 is an elevational view showing in op- .v

erative relationship one preferred arrangement of apparatus for carrying out'the method of the invention;

Figure 2 is a vertical sectional view taken substantially through the center of the variable volume cell and showing the movable piston for attaining different pressures and the stirring means rium;

Figure 3 is an enlarged transversesectional view of the cell shown in Figure 2 taken substantially along line 3 3 of said figure and looking in the direction of the arrows; l b

Figure 4 is an enlarged sectional view illustrating the internal construction of a type of three-way valve that may be used in both the gas and the mercury manifolds;

Figure 5 is a fragmentary sectional view showing in detail the interior of the fixed volume cell pressure-liquid volume behavior of thereservoir 'fluid may -be observed and recorded from separain the perview.of the inventionto provide tor pressure to reservoir pressure. Itis alsowith` i lthe field separator.

ure the amounts of such production.- ample'c ot and the manner of connecting the mercury manifold thereto; j

Figure 6 is a graph showing one pressure-volume curve of separator gas at 210 F.;

Figure '1 is a graph showing two isothermal pressure-volume curves;

Figure 8 is a graph showing liquid phase curves illustrating the condensation lof liquid by reduction of pressure; and i Figure 9'is a sectional view showing the internal construction of a cross-angle valve suitable for use in both the gas and mercury manifolds.

'I'he apparatus of the invention has particular utility in the making of phase equilibrium deter- 'minations on recombined samples of liquid and gas of aA distillate reservoir.` When the applratus is usedfor evaluating the contents of such a reservoir samples of the liquid and 'gas pro- L duced by theswell-are collected under the conditions of temperature and pressure which exist at It is also necessaryl to measthree isothermal the liquid may be taken from the separator by the downward displacement of mercury in a suitable container. Samples of the gas may be taken from a convenient tap in the gas line leading, from the separator by purging the container and then closing the valves in such a manner as to buildup and maintain the separator pressure. In' actualpractice the samples taken from the separator are usually at pressures ranging from 400 to 1000 pounds per square inch and said samples are maintained at this pressure until `they are used in the present apparatus. The

gas-oil ratio is accurately determined from the orifice meter data showing the gas produced and form the calibration of the separator by which the actual volume of the liquid produced during the period of test may be computed. 'Ihese data together with the temperature of the separator and the temperature and pressure of the reservoir are the only eld data required in the use of the present apparatus in evaluating a gas distillate reservoir as above referred to.

The/first use to be made of the present apparatus is to obtain data as to the ccmpressibility of the gas sample. For such tests Athe apparatus includes a fixed volume cell I0, which is shown in Figure 1 in associated relation with other parts of the apparatus and in Figure in fragmentary cross section to illustrate the internal construction of the cell. The information as to compressibility of the gaseous phase is required for the precisemeasurement of the volume of gas to,

be injected, in accordance with the invention, into the equilibrium cell 20, Figures 1 and 2. The latter mayfbe termed a variable volume cell in order to distinguish froml cell I0. The cell I0 is immersed in oil within receptacl II and the electric heating unit I2 is provided for heating the oil to desired temperatures, which are thermostatically controlled by the thermoregulator I3. The motor T4 provides a dependlngarmature shaft to which is secured the stirring propellers I5. The cell I0 at its upper end by bolts 29 and which eieet a. hermetic seal between the two parts by means of the interposed gasket 30. r'I'he upper portion 21 containis connected to a gas manifold, to be presently described in detail, by means of valve I6 and conduit I1. The bottom of the cell, as best shown .in Figure 5, is equipped with a connection I8 which extends through the bottom Wall of the receptacle II, being joined by the nipple I9 with a mercury manifold'sov that mercury may be ilxlijected. into the bottom of the fixed volume cell I y is injected into the variable vvolume cell 20 along with a definite amount of liquid to produce reservoirmaterial equivalent to that which entered the well bore from-the formation during sampliage. In the variable volume cell a number of ing the floating piston 3| is closed by the head 32 andby the retaining member 33 which iits over the head. having threaded connection with cylinder 21. By tightening the bolts 34 the cylinder head may be forced against the interposed gasket 35, thereby making a mercury-tight closure. The piston rod 36 passes through the cylinder head, which is provided with a packing y A gland 31. Said piston rod at its upper end carries an index pointer 38 which moves along the scale v39, thereby indicating to the nearest cubic centimeter the volume of space within the cell 20 below the piston 3|. v

Within the lower portion 28 of cell 20 there is located an electric motor 40 having an armature shaft depending therefrom to which is secured the large propeller 4I and the relatively small propeller 42, the latter being located within the bore 43 provided in the lower portion 28 of the cell. Large propeller 4I thoroughly agitates and mixes the gas below piston 3| and the small propeller is located at the extreme lower end of the shaft so as to project into and stir the liquid within bore 43. By means of this stirring equipment all portions of each phase, that is, the gas and the liquid, vmay be brought into intimate contact with each other so that equilibrium between them may be established in a short period of time. Bore 43 in portion 28 of the cell is provided with a relatively small slot 44 extending for approximately three-fourths of the length of the bore and which leads to the exterior so that the bore is thus opened by the slot.

In accordance with the invention the cell 20 is provided with visibility features whereby the liquid phase of the reservoir material within the cell may be observed. The slot 44 is therefore closed by the glass window 45 which is in contact with a slotted gasket 46. On the front side of this glass window there is positioned a similar slotted gasket 41 and said gasket and the glass window are securely held in position by the rectangular metal plate 48 bolted to the portion 28 of the cell by means of bolts 49. Adjustment of plate 48 is effected by the set screws 50. The interior of bore 43 is visible through Window 45 phase equilibrium determinations are made on Y said resultant mixture. The cell 20 is suitably supported within a cylindrical receptacle 2 I, substantially filled with oil providing an oil bath for the c'ell 20 since the cell is immersed in the oil. The'bIath may be hea-ted by the electrical heating-unit v22 thermostatically controlled by the thermo-regulator 23e-so that the bath may be vheated yto the temperature desired and maintained at said temperature for the proper period. The electric motor 24, by means of its depending shaft 25 and the propellers -26, thoroughly stirs the heated oil within receptacle 2l to assure a uniform temperature throughout the oil bath.

--Reterring to Figure 2,. the variable volume cell retaining plate lIIB. accordance with the foregoing has been safely tested to seven thousand pounds per square inch at 280 F. However, in case of breakage of the glass the possibility of injury to the operator is negligible due to the very small unsupported area comprising the slot. It is impossible for an explosion to occur in a lateral direction nor canthe gasket blow out toward the top or bottom as the ends are confined within the solid metal of the lower portion 28 of the cell.- This window provides means whereby the operator may observe the liquid gas interface of the reservoir material with-A in the cell and also the mercury-liquid interface which during operation of the apparatus is positioned at some pointlongitudinally of the bore 43. The small cross sectional area of bore '43 has the effect of increasing the length of the co1- umn of liquid and by means of a line scribed on A window constructed in the cylinder walls.

and gas volumes. The presence of this index on the inner face of the window eliminates the errors due to parallax which would be present if the index were on the outside.

Just above the restricted portion of cell 20 formed by the bore I3 there is provided additional windows so that the behavior of the gaseous phase within the cell may be observed by the operator. These windows are formed by the threaded cups 53 which are threaded into the cell so as to extend completely through the wall of the same. The cups are provided with an axial passage and it will be' understood that the axial passage of one cup is aligned with that of the other so that a light placed in front of one is visible from the other side of the cell. If necessary, the cups may be disposed somewhat eccentric with respect to the axis of the cell .in order that the armature shaft of motor 40 will not obstruct the passage of light. Each cup is provided with a glass window 5 4, the same being retained within the cup by means of the threaded closure 55, likewise having an axial passage aligned with that of the cup. The purpose of this set of windows is to provide a means of detecting the first formation of fog, that is, dew point of a mixture which has passed entirely through its critical region and has become a single phase system. As pressure on this single phase system is slowly reduced, the material will pass throughl a very definite point where the formation of minute droplets of liquid takes place. This "fogging will cause a sharp decrease in the amount of light which passes through the mixture and this decrease can be readily observed by the eye and by means of a photo-electric cell. This procedure eliminates the guess work in determining the 1 critical dew-point.

Referring again to the cylinder head 32 of the cell, the same has been tapped to receive a suitable tubing connector 56 which is screwed into the tapped hole. The tubing 51 supplies mercury to the connector which is therebir admitted within the cell 2|! and above piston 3| to effect movement of the piston. The piston is provided with suitable packing and retaining means 58 whereby the pressure on the packing may be adjusted. This is all that is necessary as concernsthe piston since the same is never subjected to a differential pressure greater than that necessary to move the piston in the cylinder against its own friction on In operation this pressure rarely exceeds fifty pounds per square inch differential and is easily taken care of by the packing on the piston. In addition the differential exists only during the period -of movement of the piston and is not a factor worthy of consideration during the equilibrium determinations. The effect cf the piston rod 36 is to slightly reduce the area of the top of the piston. Since the mercury above the piston has to support the thrust of the gas below, the resulting pressure of the mercury is always slightly higher than that within the gas chamber. Therefore any tendency toward leakage around the piston would be for the high pressure mercury to bypass the piston and enter the chamber below. This would not be detrimental to the reservoir fluid within the cell as the mercury can be withdrawn through the bottom connection 59, having threaded connection with the lower end of the bore I3.

The fixed volume cell |l| and the variable volume cell 20 are connected to the mercury manifold 60 by somewhat similar structure. The cell ||l has a connection I8 which extends through fold 60 may be admitted or withdrawn froml bore 43.

The several different types of valves that may be used in the present invention are shown in detail in Figures 4 and 9. In the three-way valve of Figure 4 the rotatable element 10 is provided with a diametrically extending passage 1| having a lateral passage 12. By positioning the element 10 as shown in said figure, the conduits 13 and 15 are connected and conduit 14 is closed. In other positions of element 10 the conduit 13 may be joined to 14 or 14 may bejoined to 15. The three-way valce of Figure 9 is known as a cross-angle valve, the saine having a rotatable element |10 located in the passage |1|. In this type of valve-the rotatable element closes the conduit |14 only since conduits-|13 and |15 are always in communication, being joined by passage |1|. When a cross-angle valve is used in the mercury manifold it has the advantage that the pressurelis continuously indicated by dial gauge 83 and piston gaugel since they are always connected to the mercury pump.

The gas manifold 85 is used for the transference of gas from the sample cylinder 16 to either of the cells l0, 20. Conduit-H 'from the manifold delivers the gas to and conducts the same from the cell |0. The conduit 11 conducts gas from the manifold to cell 20, and in this case the said conduit also delivers liquid to the cell from the sample cylinder 18 having connection with both the gas manifold and the mercury manifold. The manometer 19 is used to measure accurately the original pressure of the gas in cell I0.

Mercury is supplied to manifold 60 by the calibrated mercury pump and by the power driven pump 8|. The latter is used for the bulk movement of mercury from the tank 82 into either cell I0 or 20. The calibrated pump 30 injects accurate quantities into cell l0 for the compressibility measurements, and said pump is also used in measuring the exact quantities of liquid from the sample container 18 to be delivered to cell 20, and in measuring the volume'of residual manifold opposite the pumps a dial guage and a dea d weight or piston gauge 84 are provided for indicating the pressure existing in the manifold. The dial gauge indicates the aD- proximate pressure and the piston gauge gives a more accurate measurement. Y ,l

After the containers 16 and 18 for the gas and liquid samples, respectively, have been properly connected into the present apparatus, the operation of thesame is as follows:

The cell |0 and cell 20 are both thoroughly washed with petrolic ether or other suitable solvent under a pressure of from one hundred pounds to four hundred pounds per square inch. This liquid is caused to enter the gas manifold 65 and by opening valves I6 and 85 the liquid is introduced into the respective cells, thoroughly washing all residual oily material which might be left from a previous determination and which would be a source of error.v The washing soltures upy to the capacity of the heating unit I2.'

vent u withdrawn throlh valves sz and se, be-

. ing expelled through the outlet conduit `86`pro vided ffor egchof said valves. After closing the Said/outlet valves the cells I and 20 are dried '/y thoroughly evacuating them through the gas adjustedy to approximately room temperature,

isrecorded to within plus or minus .2 F. by means of an ordinary thermometer suspended in the'oil bath. By means of lthe'applicatiou of vthe gas laws to the known volume of gas under the above described conditions of temperature and pressure, the actual volume of the ysample within the cell I0 at standard conditions of 60"vv Il'. and 14.7 pounds per square inch absolute can readily be found. The object lnow is to determine ,the compressibility of this particular gas. l For the compressibility determinations an accurately measured volume'of mercury is injected into cell. I0 by means of the calibrated mercury pump 80 which requires that valve 88 beopened to said pump and that valve 63 be opened to ysfelmrreetJag@ cell with the mercury manifold.

gases begin to deviate, and the magnitude of-this deviation varies with the temperatura'pressure. and the composition of the gas. It is for the determination f this deviation factor or compressibility factor that the method above described has been'developed By continuing the method from plus ten pounds to one thousand pounds /cated approximately by dial gauge B3 and the fsame may. be accurately measured by the piston gauge 8l.Y The reduced volume and increased pressure are recorded on a suitable form by the operator. An additional measured volume of mercury is now forced intol cell I8 by pump 80 and this further reducedgas volume and further increased pressure are recorded in tabulated form with the first reading. This procedure is repeated until the gas pressure in cell I0 is of the to its actual volume at the temperature of determination. The dierences in these corrected volumes of the cell'and the Ainjected mercury give the true volumes o'f the; known amount of the gas Asample at the respective elevated pressures. This information is thenplotted and a graph is secured for the particular gas sample similar to that shown. in Figure 6, which indicates the .pressure-volume relationship of separator gas at 210i F. By draining the mercury from cell Il back into the tank 82, requiring actuation of i low mercury in back of the piston 3i to return toi per square inch, then through another `cycle starting with cell I0 lled to six hundred or eight hundred pounds per square inch and running up to approximately i-lve thousand pounds, the actual volume occupied by one cubic foot of gas at 60 F. and 14.7 pounds pressure absolute can be accurately determined at any temperature and pressure up to and including the formation temperature and pressure.

Having determined the compressibility factor or the speciilc volume of the gas, it is now possible to calculate by a simple ratio from the production data of the well during sampling, the equivalent amount of liquid to .be added to a deiinite volume of the gas to give an exact equiv-- aient mixture to that which entered the well bore from the formation during sampling. In other' words, said mixture may be considered the reservoir iiuid produced by the particular well during the sampling per-lod.

'I'he phase equilibrium determinations are carried out in cell 20. Gas from the sample container 'i8 is admitted to said 'previously` Washed and evacuated cell, valve 85 being open for the purpose. The mercury manifoldV is open" to althe reservoir tank 82. Theipiston lwill therefore. rise under the pressure of the gas and the `with.. drawal of mercury is' continued untilthepiston is very close to the top of itsI chamber when valve 92 inthe mercury manifold and valve 85 in the gas manifold are closed. The quantity of gas in cell 20 is then allowed to come to the temperature of theoil .bath surrounding the cell and this temperature is recorded as is also -the pressure of the gas indicated by gauges 83 and 8l.

For accurately measuring this pressure the mercury level in the gas chamber should be adjusted .to an 'exact level'with the zero mark I2 which can be accomplished by withdrawing 0r-inject ing the required amount of mercury through the calibratedmercury pump 80. The exact volume of the gas within cell 281s now noted' from the position of the index pointer 8l with respect to the scale 39. The Ipointer is actuated by' the I Piston rod 38 which moves with the piston 3i.

valve -88 to admit the mercury to the'vertical conduit l0 leading to the tank, the process can be repeated'at any number of 4elevated `tempera- By the plotting of one or more of these isothermal pressure-volume curves, the engineer can From the data obtained during the compresi sibilitydeterminations, this volume-pressure-temperature infomation is no w translated into cubic feet at 60 F. and 14.7 pounds per square inch absolute. With this gas 4volume known, it is now possible to calculate from the well test data, giving the number of cubic feet of gas at 60 F. and 14.7 pounds per square inch absolute per barrel of separator. liquid under separator pressure and temperature,the exact equivalent volume of liquid contained in the cylinder 18, which must be solve many of the problems of gas reserves,` coml n pressor types, and eapacities'of transmission pipe unes inthe gas lndustry.v The value or these ues in there@ that in ensineerlnework loliey-.theillllvinloi Charles and Boyle. They do L lthis with fair' aocuracyffor a .relatively kfew labove atmospheric, :but thenthe are no perfect gases', that is, those whichl added to the gas within the gas chamber of cell 2l`so that the resultant mixtureiis equivalent to the reservoir fluid which entered the bottom of.

the well from the formation during the samplingperiod.. The injection within the cell 20 of this calculated volume of liquid is done as follows:

v With valves Il and V8l closed as regardscell 28, and Lwith valve l2 closed to prevent furtherl withdrawal of mercuryfrom the upper -end of cell A1l conduitl Il, andwith valve 88 lopen, pressure is .built-up in the mercury manil -intimate contact with the other. In the course ser 88 on scale 88.

fold by pump 88 toappnxiatelythe pressure of the gas/inth' cell and the liquid in container Welt/being understood that the gas and liquid I 4"sample are each at the same or separator pressure. The valve 94 is now openedkand mercury is forced through theby-pass conduit-98 and through valve 91, which is also open so as to -admitthe mercury to the gas chamber oi' cell 28.

It is possible to obtainan indication of the mercury entering the gas chamber by means of the window 45. The pressure on the mercury manifold is then noted and valve 94 is closed. Valves 98 and A99 are now opened and the pressure in the cylinder 18 is adjusted by means of pump 88 until it is equal to the gas pressure in cell 28. In order to be sure that this is true, valve 94 is opened, with valves 98 and 99 remaining open, and any slight difference in pressure is equalized throughout the entire system consisting of cell 28, the liquid sample container 18, mercury manifold 68, gauges 83 and 84, and the calibrated mercury pump 88.

Valve 91 remains closed during the above procedure. r The exact volume, as indicated on the scale and dial of mercury pump 88,`is now read to .01 cc. and recorded. With valve 94 closed and valves 98 and 99 open,.then upper valve 91 also being'open, a path is provided for the mercury to enter the bottom of container 18 to displace an equal amount of hydrocarbon liquid from said intainer through valve 91 intothe conduit 11 and which'i'seventually injected' into cell 28. The volume of liquid calculated as alc/tobeeaddegL to the gas in cell 28 is displaced by the mercury and when the exact amount has been forced from Y cylinder 18 the valves are closed. To drive out the last remaining quantity of liquid from conduit 11 valve 94 is opened and mercury is forced bybumpmthrousblllellyjass collduit 9 and into said conduit 11 so that alltle/ liquid 'isdisplaced by the mercury, whichA forces the samey into cell 28. When the dropping of mercury lfrom the inner end of conduit 11 is visible from win-4 dow 45; the valve 94 is closed and the cell 28 is ready for the phase equilibrium determinations.

the ze/ro/index'ad the reading of pump 88 is again' recorded. V

The difference between-this last reading and previous ones, after the application of-acorrec` tion, due to the capillary displacement of the menisci, is recorded as the volume of equilibrium liquid at the observed temperature, pressure and equilibrium gas volume. The power driven mer- Y cury pump 8| is nowstarted and by closing certain valves and opening others mercury can be pumped into the upper end of cell 28 above the piston 3|v to force the piston downward, thereby compressing the gas-liquid mixture within the gas chamber. At intervals the pump 8| may be stopped-and the pressure ,on the Amanifold noted so as to secure an indication as to the approximate pressure rise within the gas chamber. When thepressure has been raised from fifty to two hundred pounds per square inch above the preis continued until the maximum pressure desired "btheoperatorisobtained. The result of this The said determinations are usually run at three temperatures, one at approximately atmospheric, one at approximately 125 F., and one at the temperature of. the reservoir.` 'The oil bath surrounding cell 28 is brought up to the desired `temperature by means of the heating unit 22, and the same is maintained constant by ther thermo-regulator 28. AAs soon as the desired ternperature is reached stirring motor 48 withincell 28 is started. `With lone propeller located in the gas chamber and the other located within bore 43 so as to 'contact the liquid, both phases of the reservoirmaterial are agitated `to bring each into of approximately two to three hours complete equilibrium between them is' achieved. The motor 48 is then stopped. its heat isallowed to dissipate, and the mercury level is adjusted until the lowest point of theliquid-gas interface is exactly level with the zero mark 82.- This lis done by opening valves 88 and '88 and manipulating the piston o f pump 88. The exact pressure exerted by the mixture within cell 28 is determined by means of dial gauge 83- and piston or dead weight gauge 84.' The `Vvolume of the gas phase is determined .by noting the position of the point- Then thereading of the mercury pump 88 is recorded.4 Mercury is now lnjected by said pump until the topmost positionpf the liquid-mercury interface is exactly opposite procedure using the presentapparatus has been referred to as the phase equilibrium determinations;

The tabulated data with all necessary corrections is finally plotted on embase-equilibrium graph, see Figure 8, in which the vertical scale represents barrels roi equilibrium liquid per one million cubic feet of gas at F. and 14.7 pounds per square inch absolute, and the horizontal scale represents absolute pressures inv pounds per squareinch. The tabulated data then forms an isothermalv lineoi theV reservoir fluidl in equilibrium.'v Additional isotherms are determined in the same manner as described and on the identiycal sample. Operation of the apparatus for determining these additional isotherms is as follows:

Valves 92 and 89 are opened to permit themercury contained in the upper portion of cell 28 in back of piston 3| to return to tank 82, which takes place automatically as the gas pressure within, the chamber will force the piston to the top of the cell. This lowering of the pressure will cause 'a precipitation of liquid from the gas phase. The liquid is allowed to drain down the sides of the gas chamber while the temperature of the oil bath is raised to the next temperature level Following this, the second set of pressure-volume data for the gas and liquid is accumulated.- This data. may be 'plotted on the same graph as the first. The resulting graphwill appear very much as in Figure 8, showing three isothermalliquid phase curves. A graph such as shown in Figure '7 may also be plotted from the data obtained as above described, which' indicates the pressurevolume relationship of reservoir fluid.

The information about the behaviorof a reservoir material obtained bythis apparatus eliminates many of the errors inherent in other devices. First and foremost of these is the integrity of the sample. A high pressure. wet sas This procedure ofl rrising Vthepressure^"'V y a assd'osa pressure under which they exist in the reservoir.

As these reservoirs are produced, both' the temperature and pressure are 4reduced as the material cornes up the well bore. This upsets the equilibrlum of the material and causes a precipitation of a large part of the heavy hydrocarbons-in the form of liquid. 'I'his liquid may exist in the well -bore in the form of liquid slugs, or as a liquid iilm on the walls of the flow string, or as a mist or tog in the gas stream, or a combination' of all three. As a result of lthis condition, attempts to sample this unstable and non-uniform mate rial by diverting a small quantity through a mini ature separation plant provides the opportunity 'for serious error.I This possibility yiseliminated precipitation of liquid occurs, the materials are relatively stable and can be handled in the laboratory with considerable ease.

With respect to the present apparatus, it should be noted that any number of phase equilibrium determinations can be made on one sample of material. These determinations are therefore comparative because they are made on the same sample. Also as a result of the visibility features' of the cell 2l the phases of the reservoir material may-be actually seen, and questionable readings can be checked for accuracy at any time im tothe discarding-of the sample.

Another advantage of the present apparatus is. that aite'rv all theA required graphical data have beenobtained, it is entirely feasible to secure equilibrium `at any point of temperature and pressure, and withdraw for analysis a sample .of the liquid or gas. or both,` thus answering the speciic question of composition at one critical vpoint of equilibrium. Additional analyses can bemade by preparing additional mixtures o! liquid and gas in the cell.

A further advantage of the improved apparatus resides in the fact that the measurement of the volume of separator sas within cell 2l is made on the basis of actual determined compressibility of that gas and not upon a value calculatedby means of critical data from the analysis. There is reason .tol believe that calculated compressibilities are subject to errors By using the actually determined compresslbility such errors are circumvented. The behavior of the material under temperature and pressure is determined instead of attempting to predict its behavior from necessarily incomplete data.

In this connection, an alternate method isdisclosed which may be usedto determine vcompressibility ofv gas at elevated temperature and pressure where onlyione set of data is required.

' ,Incases where the entire compressibility curve pounds above atmospheric. and at approximatetemperature.' This volume is converted bath is then heated to the desired-temperature after which mercury is pumped into the cylinder il by power pump until the resultant pressure,

as indicated by piston sage, is at theI desired. point. As soonas theentire cylinder, mercury.v

and tank assembly are uniformly at the desired temperature. as indicated by a 'stable pressure.

the true volume occupied by the known quantity of gas at the new conditions of temperature and pressure is determined. This is possible by displacement oi! the compressed gas with a meas'- ured quantity of mercury from volumetric pump, maintaining the pressure and temperature at the above attained level during displacement. Under these conditions, the cylinder il is already expanded by heat and pressure, and the eilects oi heat and pressure on the mercury is stable. The only variable for which correction must now be made is the increase in volume of the mercury used to displace the gas due to the increase in temperature from room to the oil bath. `This method is much more rapid as only at one point must the compresslbility be determined; the

`maior.part of-the pumping is done by power means, and ,only one volume measurement need be made; this one volume corrected for but one change inl condition, namely, temperature.

The invention as hereinaboveset forth may be variously embodied within'the scope of the following claims.

Whatisclaimedis:

l. In apparatus of the character described, a cylindrical member having a movable piston to provide a gas chamber of variable volume below the piston, the lower end of saidgas chamber .comprising a, bore oi smaller diameter than the remainder of the chamber, the cylindrical wall of the member having a longitudinal slot forv substantially the Vle `th of said bore of smaller diameter, a glass w 'retained by said member so as to close and seal the said slot whereby material within said bore is visible from the ex'- terior of thefmember, means for admittinga .gas to thevariable'volume chamber below the piston, conduit means for connecting the interior of said bore in the base thereof with a source of mercury supply, and similar conduit means for f connecting the interior of the member above the .piston with the same source of mercury supply.

- 2. In apparatus of the character described, a cylindrical member having a movable piston to provide a gas chamber of variable volume below the piston, the lower end of said gas chamber comprising a bore 'of smaller diameter than the remainder of the chamber, the cylindrical wall of the member having a longitudinal slot i'orsubstantially the length of said bore of smaller diameter, a glass window retainedA by said member so as. to close and seal the said slot whereby mau,

terial within said bore is visible from the exterior of the member, a pair of glass sealed openings provided in the wall ot said member above the bore for viewing the material in the gas eham ber, means for admitting a gas to the variable volume chamber below the piston, conduit means forV connecting the interior of said bore in the basethereoi with a source 'ot mercury supply. and similar conduit means for connect- 4ingthe interior o! the member above the piston with the same source of mercurysupply.

3. In apparatus of the character described, a.

lcylindrical member having .a movable piston to 7 to volume et w n. and 14:1# rilasciate 'ma ou of the member into compri-sing a boreof smaller diameter than "the remainder of the chamber, the cylindrical wall of the member having a. longitudinal slot for. substantially the length of said bore. of smaller diameter, a glass window retained by said mem-g,

ber so as to close and seal the said slot whereby material within said bore is visible from the exber comprising a bore of smaller diameter than the remainder of the chamber, the cylindrical i wall of the member having a longitudinal slot for substantially the length of said bore of smaller diameter, a glass window retained by said'member so as. to close and seal the said slot whereby material within said bore is visible from the lexterior of the member, means for admitting a gas to the variable volume chamber below the piston, a sealing gasket positioned between the glass window and'the wall of the cylindrical member, said gasket also having a -slot substantially aligned with the slot in the member, and a mark on said glass Window providing a zero mark for. use in the volumetric measurements of the material within the bore.

5. A variable volume cell 'fol` use in analyzing asados:

thy member for connecting-,the vsmall diameter bore with a source of mercury-supply, a conduit secured to the cap for supplying the compartment above the piston with mercury from said source, said bore below the piston forming` a chamber therewith and which has communication with the small diameter bore, means for admitting a gas to the gas chamber below the piston, said member having a longitudinai'slot ber having a bore extending internallyI of the same from end to end, said bore including a major portion of large diameter and aA portion below the same of small diameter, a' movable p iston within the member having association with the large diameter portion of said bore, a cap removably secured to the top of the member thereby forming a compartment above the plston, a piston rod secured to said4 piston and extending through the cap, a valved itting secured -to the baseL of the member for connecting the small diameter bore with a source. ofA mercury supply,l a conduit secured to the cap for supplying the compartment'above the piston'with mercury from said source, s'ald'bore belowJ the piston forming a chamber therewith and which has communication with the small diameter bore, and 'a second conduit extending through the wall said chamber for supplying a iluid thereto.

6. A variable volume cell for use in analyzing reservoir fluid comprising, la cylindrical member having a bore extending internally of .the same from end to end, said bore includinga major por-` tion of large diameter and a7 portion below thesame of small diameter, Ya movable piston within the member and having association with the large fdiameter portion of said bore, a. cap removably secured to the top of the member thereby forming a compartment above the piston, a piston rod for the greater portion of the small diameter bore, anda glass window retained by the member so as to close and seal said slot whereby the material in the small diameter bore is visible from the exterior of the member. 1

7. A vvariable volume cell for use -in analyzing reservoir fluid comprising, a cylindrical member having a bore extending internally of the same from end to end, said bore including a major portion of large diameter and aportion below the same of small diameter, a movable piston within the member havingassociation with the large diameter portion of said bore, a cap re movably secured to the top of the member thereby forming a compartment above the piston, a piston rod secured to said piston and extending through the cap, a Valved fitting secured t0 the base of the member'for connecting Vthe small diameter bore with a source of mercury supply, a conduit` secured to the cap for supplying the compartment above the piston with mercury from said source, said bore below the piston forming f a chamber therewith and which has communication with the small diameter bore, a second conduit extending through the wall of the memberinto saidl chamber for supplying a duid thereto, an electric motor positioned within the gas chamber and having an armature shaft extending within the small diameter bore, and propellers fixed to said shaft and located in the gas chamber and in the small diameter bore respectively.

8. A variable volume cell for use in analyzing lreservoir fluid, comprising, an elongated member having a bore extending through the same, said bore including a major portion of large diameter and a portion below the same of small diameter, a movable piston located within-the large diameter -portion of said bore to thereby form a chamber below the same including the A bore of small diameter, a window extending 10ngitudinally of said small diameter bore whereby. the interior of the chamber is visible,i other windows located in the member substantially diametrically thereof for viewing the interior oi the chamber, a conduit extending through the wall ofL the member into said chamber for supplying a fluid thereto, and conduit means connected-to the top and bottom of the member for supplying a pressure medium above the piston and to the small diameter bore respectively. i

9. A variable, volume Vcell as ndefined by claim 48 additionally including an electric motor' located in' the chamber, an armature shaftv extending from the motor wwlthi-n the bore f :man diameter, and propellers fixedto said shaft and located 4in .the large. diameter bore and in the small diameter bore respectively.

J. PAUL SLOAN.

CERTIFICTE OF CORRECTION. Patent No. 2,580,082. July lO, l9li5.

JAMES PAUL SLON.

It is hereby certified that error appears in the printed specification of the Vabove numbered patent requiring Correction as follows: Page L, sec- Vond column, line 55, after "residual" insert --liquid in cell 20. At the end of the mereury--g page 7, first column, line 75 before "cylinder" strike out "of" and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the oase in the Patent Office.

Signed and sealed this 20th day of November, A. D. l9LL5.

Leslie Frazer (Seal) First Assistant Commissioner of Patents CERTIFICATE OF CORRECTION. Patent No. 2,580,082. July lO, 19LL5.,

JAMES PAUL SLON.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page L, see- -ond Column, line 55, after "residual" insert --liquid in cell 20. At the end of the mercury; page 7, first column, line 75 before "cylinder" strike out "of" and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the oase in the Patent Office.

Signed and sealed this 20th day of November, A. D. l9h5.,

Leslie Frazer (Seal) First Assistant Commissioner of' Patents 

